Use this empty vial and fill up on some moonwell water here in Auberdine. Such potent magic should provide a clue as to the composition of the crystal. To do that, you'll pour the liquid over the crystal; it should take care of the rest.
While I don't anticipate anything bad happening to you, I still want you to be careful. Above us to the east is Felwood; if that crystal is tied to that place as I suspect it is, then it could prove to be very dangerous.

You have made it once more to the mysterious crystal. Removing the stopper on the tube of moonwell water, you gingerly pour the contents out over the top of the crystal. As the water cascades down its lattices, you see the opaque surface turn transparent...